Love waynes-
A genuine set if mix and matched used pistons, a good set of used straightened reconditioned rods, welded and rewelded cranks, matched heads (ford for fords, gm for gms), all this for a non warranty-able jetboat mota?

Id trust a used 100,000 mile BBC out of a dually/suburban first.

theres your marine clearances
Or build it yourself, Its not rocket surgery or brain science, just a chebby.
What went wrong on that 454? maybe fix and refresh?
Thats all I got
Daniel